Al Gore, Greenpeace, and the “consensus of scientists” tell us that global warming endangers agriculture and global food security. A study published last week in Science magazine finds global warming has taken significant bites out of potential global corn and wheat production since 1980.

The study also finds, however, that climate change has not adversely affected U.S. corn and wheat production. How so – because of Yankee ingenuity? Not according to the study. The explanation, rather, is that America has been a “notable exception” to climate change. The USA “experienced a slight cooling” during the study period (1980-2008).

This is bizarre. Here we have an alarmist study that finds a “lack of significant climate trends” in the USA for the past 30 years. If true, that makes hash out of all those dire pronouncements by Gore and others that global warming is already contributing to hurricanes, tornadoes, snow storms, forest fires, floods, etc. in the USA. Are the study’s authors aware of this implication? Are the editors of Science? Apparently not.

How do the authors know that climate change is depressing corn and wheat production globally, even if not in the USA? The biggest loss in wheat production, according to the study, is in Russia. Do they adjust Russian crop yields for the Russian economic meltown and financial crisis of the 1990s? As far as I can tell, they don’t. I would not bet the farm on the validity of this study.

Published last Friday in Science magazine, Climate Trends and Global Crop Production Since 1980 estimates that, had global temperatures remained at the 1960-1980 average, global corn and wheat yields would have been 3.8% and 5.5% higher during 1980 to 2008.

The study is getting plenty of buzz on the Web. “Climate change shrinks global crop yields, study finds” - Care2.Com.  “Global warming already affecting crop yields” - SustainableBusiness.Com. “Crop yields fall as temperatures rise” – New Scientist.  “Study: climate change cuts into global crop yields” – DeMoinesRegister.Com.  ”Cereal killer: Climate change stunts growth of global crop yields” – Scientific American.

ScienceNews.Org (“Warming dents corn and wheat yields”) captures the alarmist flavor of the study and the coverage it is receiving. Some excerpts:

Set a place at the table for climate change; hotter weather may have already taken a bite out of food crops worldwide.

Farms across the planet produced 3.8 percent less corn and 5.5 percent less wheat than they could have between 1980 and 2008 thanks to rising temperatures, a new analysis estimates. These wilting yields may have contributed to the current sky-high price of food, a team of U.S. researchers reports online May 5 in Science. Climate-induced losses could have driven up prices of corn by 6.4 percent and wheat by 18.9 percent since 1980.

The researchers tracked country-by-country yields of these common foodstuffs over nearly three decades. Harvests of corn and wheat have climbed steadily since 1980 due in part to technological advancements, says David Lobell, a land-use scientist at Stanford University. But based on the team’s statistical analysis, farmers could have produced a lot more food if the weather had been cooler. For corn, global losses amount to millions of tons — about equal to Mexico’s yearly production of the crop. “For every decade of climate change, it sets you back a year,” Lobell says.

Two things to note right out of the box. First, the study does not say that global crop production is lower today than it was in 1980. Rather, it contends that global crop production would be even higher today had there been no global warming.

Second, since many factors besides temperature and precipitation affect crop production, the validity of the study depends on how skilfully the researchers adjusted crop production data for non-climatic factors.  “Among the largest country-specific losses was wheat in Russia (-15%),” according to the study. Smack dab in the middle of the study period (1980-2008) was the collapse of the Soviet Union in 1991 and the ensuing economic contraction and financial crisis, which persisted through 1998. As my colleague William Yeatman points out, the study makes no mention of these emphatically non-climatic influences on Russian agriculture.

In contrast, the USDA featured those political and economic circumstances in its 2003 assessment of Russian agriculture:

The Russian agricultural sector is struggling to rebuild as it transforms itself from a command economy to a more market-oriented system.  Following the breakup of the Soviet Union in 1991, large State farms had to contend with the sudden loss of heavy government subsidies.  Livestock inventories declined, pulling down demand for feed grains, and the area planted to grains dropped by 25 percent in less than ten years. The use of mineral fertilizer and other costly inputs plummeted, driving yields downward.  Most farms could no longer afford to purchase new machinery and other capital investments. After about ten years of decline, Russian agriculture began to show signs of modest improvement. [Emphasis added.]

Source: USDA, Russia: Agricultural Overview

Now, what is truly curious about the Science study is that global warming appears to have had no statistically significant effect on wheat production in the United States and Canada and almost no discernible effect on corn production in North America. In the chart below, red indicates countries where climate change (supposedly) had an adverse impact on wheat production while blue indicates countries where climate change had little or no effect.

The researchers — David Lobell of Stanford University, Wolfram Schlenker of Columbia University, and Justin Costa-Roberts of the National Bureau of Economic Research — describe the United States as a “notable exception” and an “important exception.”

What accounts for this new form of American exceptionalism? You might assume it’s our Yankee ingenuity — the technological prowess of U.S. farmers. Surprisingly, the researchers say it’s because U.S. cropping regions experienced a “slight cooling” since 1980. Later, they write that “the country with the largest overall share of crop production (the United States) showed no effect due to the lack of significant climate trends.”

The Vancouver Sun (“Climate change hardly visible in North America: Canada, U.S. buck trend, scientists say”) explores this aspect of the study:

Scientists from Stanford and Columbia Universities said Canadian and U.S. temperatures since 1980 have changed, but are still within the range of “natural variability” in weather. So in North America, the effects of climate change are practically invisible. “A notable exception to the (world’s) warming pattern is the United States,” they write in a study published Friday.

Co-author Wolfram Schlenker of Columbia University in New York City said in an interview that the record is “pretty much identical” in Canada. “Overall I would say it’s pretty much the same story.”

The study deals only with agricultural latitudes, not the Arctic, where scientists are in widespread agreement that warming has begun for real, melting glaciers and sea ice.

In a summary of the work, Science notes “there’s a startling exception to the data (i.e. of global warming): the United States isn’t getting hotter, nor are its crops decreasing. The rapid agricultural changes seen in the rest of the world have not been seen in the United States.”

Although the study will surely be touted by the sky-is-falling lobby, it implicitly contradicts much that alarmists have been preaching.  For two-plus decades, the global warming movement has tried to implicate greenhouse gas emissions in every weather-related disaster anywhere in the United States. Alarmists claim to discern greenhouse fingerprints in hurricanes, tornadoes, floods, forest fires, drought, big snow storms, heat waves, and other manifestations of what they are pleased to call ‘climate disruption.’ Dr. Kevin Trenberth of the National Center for Atmospheric Research (NCAR) goes so far as to argue that greenhouse gas emissions should be presumed guilty of  contributing to every extreme weather event until proven innocent.

Yet according to the Science study, from 1980 through 2008, climate change in the United States remained within the range of natural variability.

That puts the study out of step not only with Al Gore, Greenpeace, and Dr. Trenberth, but also with the U.S. Global Change Research Program. The chart below comes from the USGCRP’s June 2009 report, Global Climate Change Impacts in the United States (p. 27). It shows more warming in the USA than in the planet as a whole. If so (and if corn and wheat are as temperature-sensitive as the Science study authors assume), then U.S. corn and wheat production should be among the most adversely affected by climate change. Yet, according to the Science study, U.S. corn and wheat production have been among the least affected.

So is the United States warming more rapidly than the rest of the world, as the USGCRP claims, or is America a “notable exception” to global warming, as the Science study contends?

I do not profess to know which assessment is correct. What I can say is that neither the authors of the Science study, nor the editors of Science magazine, nor any of the review articles referenced above address or even acknowledge the discrepancy.

The Science study should confound climate activists more than it gratifies them. If the United States is a ”notable exception” to climate change, then claims that global warming is already taking a toll on U.S. public health and welfare are hard to swallow.